timeouts on authentication should be detected

[kmccurley]

if a user sits on the "existing"/"new" choice for too long, then authentication will timeout. We need to detect this because at the moment it just shows an empty list.

[kmccurley]

I attempted to fix this on the server side by extending the timeout for PHP session cookies. There are two ways to do this:

1. change the global setting. This would also extend the timeout on the conference registration system (which I believe is the only part of the site that uses PHP sessions).
2. change the path for the session cookies on this app and extend the time in the code. This has the unfortunate side effect that it immediately logs everyone out from the app. In order to use this, we need to first push logic that handles authentication timeouts gracefully and shows the modal for logging in again.

[kmccurley]

We've addressed this partially by introducing auto-save. It's also a duplicate of #205